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The invention disclosed relates to dynamic load-rate relationships for individual, as well as for multiple fluid control devices that operate as a fluid sub-system or larger fluid system, such as pressure sensitive gas-lift valves used in the production of hydrocarbons, and more specifically to methods that describe, compare, and contrast the dynamic loading characteristics of these devices to improve the operation of such fluid systems and to ensure that such fluid systems are appropriately designed.
Approximately 10% of the daily world oil production is generated by pressure sensitive gas-lift valves in approximately 60,000 wells worldwide. Gas-lift valves are also used to unload fluids that accumulate in new and existing wells in order to start oil and gas wells flowing and to increase the production of oil and gas. In addition, gas-lift valves are used to assist in the disposal of waste fluids in fluid disposal wells.
Technology to produce fluid from wells by air-lift or gas-lift has been available to the petroleum industry for more than one hundred years. From the inception of air-lift or gas-lift valve use, testing and evaluating these valves has been a complex and costly process. Current Art describing gas-lift valve systems to produce hydrocarbons usually requires more than one gas-lift valve for a single well. Multiple gas-lift valves, for example, ten valves, may be needed to produce hydrocarbons from a specific underground formation. These fluid control devices deteriorate during their use as a result of many environmental and operating conditions into which the valves are placed.
U.S. Pat. No. 6,591,201 (Hyde) dated Aug. 7, 2003. Fluid Energy Pulse Test System [FEPTS] describes new equipment and methods to evaluate efficiently the performance of fluid control devices, such as gas-lift valves, by short duration energy pulses. The FEPTS technology describes test chambers and related fluid systems, and computer automated methods that can determine valve dynamic characteristics, including, opening pressure, closing pressure, flow rate, valve flutter, bellows characteristics, and leaking components. Patent application Ser. No. 10/259,970 (Hyde), Fluid Energy Pulse Test Systemxe2x80x94Transient, Ramp, Steady State [FEPTSxe2x80x94TRS] describes improvements to the FEPTS apparatus and methods to generate temperature-controlled and acoustically monitored transient, ramp, constant-steady-state, and periodic-steady-state test data by explosive regulation of fluid pressure and fluid flow rate for fluid control devices under test.
U.S. Pat. No. 6,591,201 and patent application Ser. No. 10/259,970 in their entirety, are incorporated herein by reference, and are referred to collectively as FEPTS. The Art described by these inventions teaches how to generate test data for fluid control devices such as individual gas-lift valves that are commonly described as tubing retrievable [TR] or wireline retrievable [WR] injection pressure operated gas-lift valves [IPO-GLVs] or production pressure operated gas-lift valves [PPO-GLVs]. The circular dimensions of pressure sensitive fluid control gas-lift valves of varying lengths are standardized by industry with outside diameters of 1.5875 centimeters (five-eighths inches), 2.54 centimeters (one inch), and 3.81 centimeters (one and one-half inches).
When a well is to be operated by gas-lift valve technology, each individual valve in a string of valves must be sized to pass a required amount of fluid through the valve. Gas-lift valve strings lift fluid in wells either intermittently or continuously, depending upon the fluid producing formation properties. Sizing a gas-lift valve includes determining a port size, opening pressure, closing pressure, fluid flow rate, and valve load rate. Each gas-lift valve is placed in a well to perform its function of assisting in the lift of the well""s economic fluid.
With current Art, when each valve in a gas-lift valve string is sized to conform to a gas-lift valve lifting design scheme, the resulting system may function excellently, moderately, poorly, or not at all. Inadequate or sub-optimal operation is a result of the current inability to compare and contrast the operation of individual valves in a string of valves before they are placed into a well. It is common practice in the petroleum industry to over design gas-lift valve strings so that some fluid will flow. As much as 200% error in the design of lifting parameters can occur. Common practice and economics dictate that if a gas-lift well is flowing, gas-lift valve parameters are not changed even if the lifting program is substantially sub-optimal. The principal gas-lift valve parameter that specifies how a gas-lift valve will function to open, close, and pass fluid is called the valve load rate.
The load rate of a gas-lift valve is determined by procedures described in the American Petroleum Institute Recommended Practice for Testing Gas-Lift Valves, 1995 and API Recommended Practice 11V2, Second Edition, March 2001. A gas-lift valve is subjected to small changes in pressure as the distance of valve-stem travel is measured. Stem travel from fully closed to fully open is commonly in the range from zero to 0.254 centimeters (0.100 inches) or zero to 0.508 centimeters (0.200 inches). By changing pressure, a graph of valve-stem travel with respect to pressure can be generated. This graph commonly shows a linear characteristic with dimensions of kPa per centimeter (psig per inch). When valve-stem travel is measured by increasing then decreasing pressure, a hysteresis effect occurs. The increasing and decreasing pressure paths of valve-stem travel with respect to pressure are averaged to generate a numerical load rate, for example, 1397 kPa/centimeter (500 psig/inch).
The evaluation of a gas-lift valve load rate is time consuming, requires some valve disassembly and special equipment to monitor stem travel, and applies only to the specific gas-lift valve evaluated. The gas-lift valve load rate data are extrapolated to include all gas-lift valves manufactured to the same specification under various pressure conditions. Thus a benchmark criterion is generated to create a valve load rate.
A gas-lift valve""s load rate is closely related to the valve""s parameter settings for opening pressure, operating pressure, closing pressure, and fluid flow rate. When a gas-lift valve is configured for a gas-lift valve string, the common practice is to set the valve""s bellows-dome pressure, the valve""s-spring compression, or where applicable, a combination of dome pressure and spring compression. The load rate test is a static test and the petroleum industry has standardized load rate test criteria. For nitrogen charged valves, the nitrogen dome is charged to a pressure of 5617.1 kPa (800 psig), 8274 kPa (1200 psig) and in a separate test, to the manufacturer""s maximum charge pressure. All pressures are referenced to 15.56 degrees Celsius (60 degrees Fahrenheit). For spring loaded valves, the spring compression is set to provide the manufacturer""s maximum recommend set pressure. Specialized equipment requiring some valve disassembly is used to measure stem travel with a micrometer probe. Data are taken at different pressures and a load rate for the gas-lift valve is obtained by averaging the test results. A single numerical load rate value for a valve is generated in units of kPa per centimeter (psig per inch).
Each valve in a string, manufactured under the same specifications, is assumed to follow the load rate data generated by a benchmark load rate test. Gas-lift valve strings with multiple valves are then designed by selecting a gas-lift valve with a specific port size and setting each individual valve in a string to its design opening pressure. These static activities do not provide any information about how a gas-lift valve functions dynamically in the system of gas-lift valves designed to lift fluids. There are no dynamic properties available that are associated with the individual valves or with a string of valves.
In practice, current Art to improve hydrocarbon production by gas-lift involves addressing many well-field activities. Studies to improve well-field operations commonly assume that the gas-lift valves strings are working properly. For example, for well-fields, two types of techniques are used to analyze gas-lift installations. These techniques are named the detailed methods and the observation methods. Detailed methods include acquiring flowing pressure surveys, flowing temperature surveys, fluid level soundings, and surface casing and tubing pressure variations. Observation methods include monitoring surface back pressures, total fluid recovery, injection gas volumes, total produced gas volumes, operating injection pressures, and temperatures of flow lines. However, a generally accepted petroleum industry practice in operating gas-lift well-fields is to wait until trouble occurs before analyzing the gas-lift installation, which leads to the problem that without prior knowledge of the dynamic characteristics of each gas-lift well, changing the design of one or more wells involves guesswork.
As a result, the current Art suffers from a number of disadvantages.
(a) There are no efficient, cost effective methods to compare static and dynamic operating characteristics of individual gas-lift valves that function within a string of gas-lift valves.
(b) Current technology does not address the dynamic load rate of valves that are set to practical operating pressures which may be any pressure in a practical range from a few hundred kPa (psig) to 10,443 kPa (1500 psig) or more.
(c) Current Art acquires only static load rate data, which data do not provide information on fluid pressure and fluid flow rate dynamic loading effects.
(d) Load rates and load rate testing are not an integral part of the gas-lift valve string design because dynamic load rate data are hidden by simple approximations and assumptions about valve operation.
(e) The time required and equipment used to conduct a static load rate test make it impractical and costly to determine the load rate for each individual valve.
(f) There are no methods available to determine the dynamic operating properties of one valve relative to the other valves in a string.
(g) Gas-lift valve strings are known to operate in well-fields as a system of components that must function in relative relationship from one component to another but engineering designs do not expressly address the valve strings as a system because there are no practical methods available to demonstrate the relative operating relationships of one valve relative to the other valves, or one string of valves relative to other strings.
In accordance with the principles of the disclosed invention herein designated Dynamic Relative Load Rate [DRLR] For Fluid Systems, there are provided:
(a) methods to acquire DRLR test data for gas-lift valves from tests that are conducted with FEPTS equipment and techniques;
(b) techniques to evaluate FEPTS test data on valve opening pressure, closing pressure, fluid flow rate, and differential pressure rates to establish relative dynamic operating characteristics of one valve with respect to other valves in a string of valves;
(c) ways to include gas-lift valve relative dynamic load rate data in the engineering design of valve strings to improve the economic cost in operating gas-lift valve strings to lift fluids;
(d) methods to use gas-lift valve operating data to demonstrate how a valve string will function when compressor driving pressures, or field gas pressures are increased or decreased from the design driving pressure, or are subject to transient drive pressure conditions;
(e) methods to determine the value of a DRLR variable of a gas-lift valve for any pressure within the range of a few hundred kPa (psig) to 10,443 kPa (1500 psig) or to the manufacturer""s maximum operating pressure;
(f) methods to identify a failing or faulty gas-lift valve which may pass all standard tests such as tests for leaks, opening pressure, closing pressure, and fluid flow rate but which valve""s performance, relative to the other valves in a string of valves, is unsatisfactory; and,
(g) methods to identify the operating characteristics of a string of gas-lift valves relative to other strings of gas-lift valves used to produce hydrocarbons from a well-field by the direct transfer of DRLR methods to describe the loading of a string of gas-lift valves relative to other strings of gas-lift valves in a well-field.
The FEPTS describes equipment and methods to acquire and to evaluate the performance characteristic curves and operating properties of fluid control devices, including gas-lift valves. Various kinds of data are acquired by the FEPTS to evaluate the operating characteristics of individual fluid control devices such as gas-lift valves.
The invention of DRLR For Fluid Systems uses test data acquired from single or from multiple fluid control devices to determine the relative loading of a fluid control device when subjected to different operating conditions. In gas-lift valve strings, multiple gas-lift valves are used to lift fluids from operating wells. It is practical to compare and contrast the operating properties of individual fluid components, such as gas-lift valves, because the FEPTS generates appropriate comparison and contrast data quickly and economically.
As a result of the ease of operation and fast response time generated by the FEPTS, there are several methods to compare the operating characteristics of multiple fluid control devices that function as a system. Gas-lift valves that are used in hydrocarbon production are illustrated here, by example, to describe the principles upon which the comparisons and contrasts of fluid control devices are made by following methods described by the present invention of DRLR For Fluid Systems.
DRLR characteristics for individual gas-lift valves in a string of gas-lift valves operating as a system are generated from valve operating properties available from FEPTS valve performance test data. For example, properties available for DRLR comparison include: opening pressure, operating pressure, closing pressure, flow rate at various pressures, pressure rate increase or decrease across a valve port, and time of a performance event. With FEPTS equipment, test data can be obtained for open-to-the-atmosphere, partly-open-to-the-atmosphere, or closed-to-the-atmosphere test conditions. A DRLR variable for a specific fluid component in a system is defined as a ratio of operating parameters. This DRLR ratio is made up of a numerator and a denominator term. The numerator and denominator terms may be both static, both dynamic, or one static and one dynamic. Because the DRLR concept is relative loading, dynamic relative load rates with dimensions other than kPa per centimeter (psig per inch) of stem travel can be used to provide information about how a fluid component functions dynamically in relationship to other fluid components. The conventional load rate dimensions of kPa per centimeter (psig per inch) is simply one member of a much larger set of dimensions that define load sensitivity and that describe how a fluid control device, such as a gas-lift valve, functions under different loading conditions.
Formally, DRLR ratios, alternatively DRLR variables, are generated from a static numerator and a static denominator; a dynamic numerator and a static denominator; a static numerator and a dynamic denominator, and/or a dynamic numerator and a dynamic denominator. If static variables are used for both the numerator and denominator in the ratio, and are constant, the static term will be the same value for each same-component in a system. [The term xe2x80x9csame-componentxe2x80x9d means that each fluid component is manufactured to the same specification.] If a static variable is generated to approximate the load on a device from information acquired by conventional testing, a linear or other path relationship of mechanical motion can be used for a range of test pressures to provide relative loading information. Thus, DRLR ratios can be generated with a linear or other path approximation of mechanical stem travel. For different-components, the static term can be a different value for each different-component in the fluid system.
When a DRLR ratio contains two constant static terms for same-components, no information is provided about how one component functions in comparison to other components in a system.
A DRLR ratio comprising one static term and one dynamic term, provides a first method to compare the operation of individual fluid components, one relative to another, in a system of fluid components. For illustration, a static term is placed in the denominator. For same-components, the static term may be the same for each component or the static term may be a linear or other path approximation of stem travel. The numerator term then is used to evaluate the relative performance due to loading on individual fluid components. For individual components in a system to function as an operating system, the DRLR ratios will have a particular characteristic trend, which depends upon the physical properties and construction of the components. The trend may exhibit constant, linear, exponential, frequency, or other characteristics that describe the system operation by the relative comparison of how each individual component functions when working with the other components in the system. The static term will be either constant or a specific approximation of stem travel, such as a linear approximation. A relative comparison of the operation of the system is generated by the influence of the numerator term of the ratio. This approach permits normalizing dynamic load rate data so that the DRLR variables for components in the system can be compared to unity at a particular operating point of the system. In this way, groups of components can be evaluated as a system.
One example of a DRLR comparison scheme, among many DRLR comparisons schemes for gas-lift valves in a string of valves, can be created with one static value and one dynamic value. Steps to generate a DRLR variable from energy pulse test data are:
[1] select a static or dynamic denominator term that will be combined with the numerator term from one or more operating variables that describe loading, alternatively, the operating characteristics of the fluid component; if appropriate, use mathematical operations to generate one value for the denominator term;
[2] select a numerator term that will be combined with the denominator term from one or more operating variables, which describe the loading, alternatively, the operating characteristics of the fluid component; if appropriate, use mathematical operations to generate one value for the numerator term;
[3] normalize the result if appropriate; and,
[4] Choose an appropriate variable for the abscissa of a DRLR graph and plot the DRLR characteristic curve.
For example, a constant static denominator value of 0.508 centimeters (0.200 inches) may be used to define maximum valve stem travel for each valve manufactured to the same specification in a string of valves. The static denominator might be assumed to be the same for each valve. In this example, the dynamic numerator might be selected to be the difference between the opening pressure and the operating pressure of the gas lift valve. The opening and operating pressures for this comparison scheme could be derived from a closed-to-the atmosphere, open-to-the-atmosphere, or partly-open-to-the-atmosphere test procedure as described by the FEPTS.
Comparisons of the DRLR variables of the nonlinear pressure sensitive gas-lift valves are sensitive to changes in operating conditions. The initial conditions used to determine the value of each DRLR variable must be consistent; otherwise, the relative relationships among individual gas-lift valves manufactured to the same specifications cannot be assured. For example, in identifying each DRLR variable with a specific operating pressure, a comparison of four gas-lift valves with DRLR values determined from opening pressure, operating pressure, and constant stem travel of 0.508 centimeters (0.200 inches) could generate the two-tupples: [1397.1 kPa/cm, at 5617.1 kPa (500 psig/inch, at 800 psig)], [1261.4 kPa/cm, at 5272.4 (450 psig/inch, at 750 psig)], [1125.7 kPa/cm, at 4927.6 kPa (400 psig/inch, at 700 psig)], and [990 kPa/cm, at 4582.9 kPa (350 psig/inch, at 650 psig)]. These example data clearly demonstrate a linear trend. If one of the gas-lift valves is not operating correctly or if its initial conditions for evaluation are not consistent with all evaluations, the DRLR trend will not be linear because the datum for such a valve will not have an appropriate relative position, or location, among the data. This simple example illustrates one possible DRLR comparison scheme among many DRLR comparison schemes. The trend, or scatter, of DRLR data will depend upon the settings, sizing, and operating characteristics of the type of fluid device or component under comparison. Other examples of DRLR comparisons of several gas-lift valves are illustrated in the drawings.
A DRLR ratio comprising two dynamic terms provides a second method to compare the operation of individual fluid components, one relative to others. The steps to generate DRLR data with two dynamic terms from FEPTS energy pulse test data are the same as steps [1], [2], [3], and [4] described above.
DRLR ratios can be characterized for gas-lift valve strings to ensure that individual valves function appropriately as a system. DRLR comparisons based upon individual valve dynamic operating properties can be incorporated into the design of a lifting scheme and can generate new valve-string parameters to be followed when installing valve strings. When DRLR comparisons are consistent, the valve string designer can be sure that the individual valves will operate as the system is designed to operate, even with changes, within limits, in driving fluid pressure for the system.
As a result of DRLR evaluations, the economic payback for fluid control systems such as gas-lift valve strings can be improved by generating data that show how each valve will operate, relative to the other valves, within the design parameters of a string of valves, even when drive pressures are not consistent. Moreover, the DRLR invention couples test operations of a gas-lift valve to actual operating conditions in the range from a few hundred kPa (psig) to the manufacturer""s maximum operating pressure. Faulty gas-lift valves operating in a dynamic environment are identified by dynamic operating data generated from the DRLR invention. Clearly, the invention of DRLR For Fluid Systems is dependent upon methods to test and to generate fluid control device test data quickly and cost effectively. These criteria are met by the FEPTS.
Accordingly, objects and advantages of the DRLR invention are:
[1] to provide efficient, cost effective, methods to compare and contrast the operation of individual fluid devices and components that function within a system of fluid devices and components, such as gas-lift valve strings;
[2] to provide methods that permit the load rates of fluid control devices, such as gas-lift valves, to be compared for any pressure within the range of a few hundred kPa [psig] to the manufacturer""s maximum recommended pressure, and to provide methods for load rate evaluation for fluid devices and components operating in vacuum;
[3] to provide DRLR data that can be used to characterize a system of fluid control devices so that the operation of one fluid device in a system can be compared to other fluid devices functioning to establish a fluid flow;
[4] to provide methods to identify failing or failed fluid devices that may have passed standard types of tests that do not incorporate dynamic variations;
[5] to provide information about fluid devices operating as a system that can be incorporated into the engineering design of the system of components;
[6] to provide a method to show how a system of fluid devices will function when pressure and flow rate deviate from the system design pressure and flow rate;
[7] to provide an alternative method to conventional Art that uses choke valves and constant pre-set operating pressures for individual gas-lift valves to generate required flow rates, thereby creating an alternative design for gas-lift valve strings; and,
[8] to provide a method to compare, contrast, and correlate dynamic relative load rate characteristics of individual gas-lift wells in a well field so that the analysis of gas-lift well installations can be initiated while the field is being designed rather than waiting until the field is in production to initiate analysis.
Further objects and advantages of the present invention of DRLR For Fluid Systems are to provide an apparatus and methods that identify DRLR variables for fluid components in order to establish how multiple fluid components function together under both optimal design operating conditions and non-optimal operating conditions, determined by: generating graphical data of dynamic performance; acquiring dynamic relative load rate data using different fluid driving functions such as impulse, step, ramp, and frequency response functions; characterizing the relative loading of one component with respect to another; permitting evaluations within a short time; establishing the robustness of a fluid system; and, initiating new ways to define the relative dynamic properties of fluid control devices and components that function as a fluid system. Further objects and advantages will become apparent from consideration of the following descriptions and drawings.